The idea that stuck, at least in the west, came from the Greek philosophers, and it was actually something of a scientific step back. In the fourth and third centuries BCE, Plato, Aristotle , and other philosophers went all in on the notion that the planets and stars were embedded in eternally rotating celestial spheres.
For the next millennium or so, few expected the universe to have an age at all. Astronomer Johannes Kepler realized in that one major crack in the popular Greek-inspired cosmology had been staring star gazers in the face all along. A dark night sky, he reasoned , suggested a finite cosmos where the stars eventually peter out. An early version of the modern solution came, of all people, from the poet Edgar Allan Poe.
We experience night, he speculated in his prose poem Eureka in , because the universe is not eternal. There was a beginning, and not enough time has elapsed since then for the stars to fully light up the sky. He found that not only were galaxies immense and distant objects, they were also flying away from each other.
The universe was expanding, and Hubble clocked its expansion rate at kilometers per second per megaparsec, a constant that now bears his name. With the expansion of the universe in hand, astronomers had a powerful new tool to look back in time and gauge when the cosmos started to grow.
But measuring the distances to far-flung galaxies is messy business. A cleaner method arrived in , when researchers detected a faint crackling of microwaves coming from every direction in space.
By measuring the characteristics of this Cosmic Microwave Background CMB , astronomers could take a sort of snapshot of the young universe, deducing its early size and contents.
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Chelsea Gohd. The leftover radiation is known as the cosmic microwave background, and both WMAP and Planck have mapped it. In , WMAP estimated the age of the universe to be In , Planck measured the age of the universe at Both of these fall within the lower limit of 11 billion years independently derived from the globular clusters, and both have smaller uncertainties than that number. NASA's Spitzer Space Telescope has also contributed to narrowing down the age of the universe by reducing the uncertainty of the Hubble constant.
Combined with the WMAP measurements, scientists were able to make independent calculations of the pull of dark energy. Freedman lead the study that used Spitzer to refine the Hubble constant. It is quite extraordinary. Editor's Note: This article was updated on Jan. The original article stated that the oldest stars have been estimated to be up to 18 billion years old. Join our Space Forums to keep talking space on the latest missions, night sky and more!
And if you have a news tip, correction or comment, let us know at: community space. Nola Taylor Tillman is a contributing writer for Space. She loves all things space and astronomy-related, and enjoys the opportunity to learn more. In her free time, she homeschools her four children.
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